1. Field of the Invention
The present invention relates to a circuit and method for electrically supplying an electronic circuit using high frequency antenna signals.
2. Description of the Related Art
The present invention relates in particular, but not exclusively, to contactless integrated circuits operating in the presence of a UHF electric field (300 MHz-3 GHz). Such integrated circuits can be entirely passive, i.e., devoid of any autonomous source of power. They are then electrically powered exclusively using UHF antenna signals.
FIG. 1 represents a classic power supply circuit PSCT1 allowing a direct voltage Vcc to be produced using UHF antenna signals. The circuit PSCT1 consists of a charge pump PMP1 that is linked to an antenna circuit ACT comprising two conductors W1, W2 forming a dipole. In the presence of an electric field E situated in the UHF band, emitted for example by a contactless integrated circuit reader RD1, antenna signals S1, S2 appear in the conductors W1, W2. These antenna signals S1, S2 are sine-wave signals in opposite phase and of low amplitude, generally only a few tenths of a volt. They are applied to the charge pump PMP1 as pumping signals. The charge pump PMP1 then supplies a direct voltage Vcc in the order of one Volt to several Volts.
The charge pump PMP1 represented in FIG. 1 comprises three cascade-arranged pumping stages. The first stage comprises an input diode D1, an input capacitor C1, an output diode D2 and an output capacitor C2. The second stage comprises an input diode D3, an input capacitor C3, an output diode D4 and an output capacitor C4. The third and last stage comprises an input diode D5, an input capacitor C5, an output diode D6 and an output capacitor C6. In each stage, the cathode of the input diode D1, D3, D5 is connected to the anode of the input capacitor C1, C3, C5 and to the anode of the output diode D2, D4, D6, the cathode of which is connected to the anode of the output capacitor C2, C4, C6. The cathode of the input capacitor C1, C3, C5 is linked to the conductor W1 and receives the antenna signal S1. The cathode of the output capacitor C2, C4, C6 is linked to the conductor W2 and receives the antenna signal S2. As the stages are cascade-arranged, the cathode of the diode D2 is connected to the anode of the diode D3 and the cathode of the diode D4 is connected to the anode of the diode D6. At the charge pump input, the anode of the diode D1 is connected to the conductor W2. At the charge pump output, the capacitor C6 supplies the voltage Vcc. The conductor W2 is linked to the ground so that the voltage Vcc is not floating.
Upon each half cycle of the signals S1, S2, the cathode of the capacitors C2, C4, as well as the anode of the input diode D1, are taken to an electric potential higher than the potential present on the cathode of the capacitors C1, C3, C5. Thus, electric charges are transferred in the capacitor C1 by the signal S2 through the diode D1, and electric charges are transferred in the capacitors C3, C5 by the capacitors C2, C4 through the diodes D3, D5. Upon each next half cycle, the cathode of the capacitors C1, C3, C5 is taken to an electric potential higher than the potential present on the cathode of the capacitors C2, C4, C6. Electric charges are then transferred in the capacitors C2, C4, C6 by the capacitors C1, C3, C5 through the diodes D2, D4, D6. Thus, if Vs is the RMS voltage difference between the antenna signals S1, S2 and if Vd is the threshold voltage of the diodes, the theoretical voltage gain of each stage of the charge pump is equal to 2 Vs−2 Vd, i.e., for example 0.6 Volt if Vs is equal to 0.5 Volt and Vd equal to 0.2 Volt.
This method for converting UHF electric signals into direct voltage Vcc is frequently used to electrically power UHF passive integrated circuits.
The antenna signals S1, S2 are not however suited to obtaining good charge pump efficiency (ratio between the power supplied by the charge pump and the incident power received by the antenna circuit). It is indeed well known by those skilled in the art that a charge pump has optimal efficiency if it is driven by pumping signals that do not overlap, in perfect opposite phase, and preferably square in shape (voltage square waves). Otherwise, electric charges are not transferred optimally in the charge pump. Moreover, the very high frequency of the antenna signals S1, S2 favors electrical losses through various stray capacitances present between the components constituting the charge pump and a substrate on which these components are formed, generally a semiconductive substrate.
Due to these various technical and technological limitations reducing the efficiency of the charge pump, the direct voltage obtained is lower than the one that would be obtained with signals S1, S2 of the same amplitude but of lower frequency and having a form adapted to charge pumping.